1. Field of the invention
The present invention relates to a document feeding method and a document feeding apparatus which may be advantageously employed in connection with for example, a copying machine for feeding a plurality of document sheets sequentially to a document scanning area where the documents are scanned for exposure.
2. Description of the Prior Art
It is well known in the prior art to provide copying machines with automatic document feeding apparatus for automatically feeding a plurality of document sheets in sequential fashion to a document scanning area thereby alleviating the work of the operator. Documents to be copied are stacked on a document loading tray and are fed for example sequentially from the bottom of the stack. The documents are transported by means of a transport belt sequentially to the document scanning area with the document image to be copied facing the interior side of the copying machine, and the thus positioned document image is scanned for example by an optical scanning means or the like, thus accomplishing simplex (single-sided) or duplex (two-sided) copying in cooperation with the copying machine.
FIG. 1 is a cross sectional view schematically showing the structure of a prior art document feeding apparatus 201. The documents d to be copied are stacked one on top of another on a document loading tray 206. On the downstream side of the document loading tray 206 in document transporting direction 207 there is disposed a document feeding means 210 for feeding the documents d one by one in sequential fashion. The document feeding means 210 comprises, for example, a suction transport means 211 disposed beneath the document loading tray 206 and an exhaust duct 212 disposed above the document loading tray 206.
The suction transport means 211 comprises: two drive rollers 213 and 214 each having an axis extending in a direction perpendicular to the transporting direction 207; and an endless belt 215 having numerous openings therein and passed around the two drive rollers 213 and 214 which are driven by a motor m1. A suction duct 216 is disposed inside the endless belt 215. When a suction fan, not shown, is driven, suction force is generated through the suction duct 216 and the suction force is applied through the belt 215 to suck the bottommost sheet of the stacked documents D onto the belt 215. Therefore, by rotating the drive rollers 213 and 214 in the clockwise direction in FIG. 1, the documents d are fed sequentially from the bottom of the stack in the transporting direction 207.
A stream of air is blown from the nozzle of the exhaust duct 212 toward the leading edges of the documents d in the lower part of the stack. This serves to separate the leading edges of the documents and thus ensures that the documents d are fed one by one by the suction transport means 211. The document d fed by the document feeding means 210 is transported along a transport path 240 and directed into an inverting means 218.
The inverting means 218 comprises: transport paths 222 and 229; paired transport rollers 220, 221, and 230; a diverting pawl 228; and motors m2 and m3. The transport path 240 branches in the vicinity of the diverting pawl 228 into the first transport path 222 curving in the clockwise direction and the second transport path 229 curving in the counterclockwise direction.
The transport rollers 220 and 221 are disposed on the first transport path 222 and are rotatable in both forward and backward directions by means of the motor m2. On the other hand, the pair of transport rollers 230 are disposed on the second transport path 229 and are driven by the motor m3. The diverting pawl 228 is driven, for example, by a solenoid. When the solenoid is deenergized, for example, a passage is opened for directing the document d from the transport path 240 into the first transport path 222. On the other hand, when the solenoid is energized, a passage is opened for directing the document d from the first transport path 222 into the second transport path 229.
The first transport path 222 and the second transport path 229 are reunited in the vicinity of the upstream end of a transparent plate 205 with respect to document transporting direction 223, the transparent plate 205 forming a document scanning area. The document d transported through the inverting means 218 in accordance with each preset copy mode is fed along the transporting direction 223 onto the transparent plate 205.
Above the transparent plate 205, there are disposed a pair of rollers 224a and 224b each having an axis extending parallel to the widthwise direction of the document d being transported, and a plurality of endless belts 226 are passed around the pair of rollers 224a and 224b. The roller 224a is driven by a motor m4. On the inside of the belts 226 and adjacent to the lower taut portions thereof are disposed a plurality of pressure rollers 225a-225d spaced apart along the transporting direction 223. The pressure rollers 225a-225d apply pressure to press the belts 226 against the transparent plate 205, thereby keeping the belts 226 from slacking while preventing the document d fed between the belts 226 and the transparent plate 205 from lifting.
The document d transported along the transparent plate 205 by means of the belts 226 is conveyed up to the scanning position on the transparent plate 205. The document d thus transported to the scanning position is positioned with its document image to be copied facing the interior side of the copying machine so that the document image is optically scanned by an optical system, the optical scanning means provided inside the copying machine, thus accomplishing the exposure of the document image.
While the preceding document is being scanned for exposure, preliminary feeding of a succeeding document is performed. The succeeding document is transported up to a standby position just before the transparent plate 205.
When the scanning of the document image is completed, the rotation of the belts 226 is restarted to transport the document d into a transport path 236. The document d is further transported by means of transport rollers 234 and 235 and returned to the top of the stack of documents d on the document loading tray 206.
In the above document feeding apparatus 201, the transport roller 230 and the roller 224a are driven by the different motors m3 and m4, respectively. Also, since the transport speed delivered by the transport roller 230 is slower than the transport speed by the belts 226, preliminary feeding of the document d does not result in the reduction of spacing between the documents on the transparent plate 205. It is therefore not possible to reduce the total time needed to sequentially transport a plurality of documents to the document scanning area.
In order to transport and position the document first with one side thereof facing the document scanning area and then with the other side thereof facing it, as described above, there is provided, for example, an inverting means between the document loading tray and the document scanning area. The inverting means consists of a first and a second branch transport path provided between the document loading tray and the document scanning area. For simplex (single-sided) copying, the document fed from the document loading tray is turned over by passing through the first transport path and then transported with the image side thereof facing the document scanning area.
On the other hand, for duplex (two-sided) copying, the document fed from the document loading tray is first transported into the first transport path in which the transporting direction is inverted, and is then directed into the second transport path, after which the document is transported to the document scanning area. As a result, the document is positioned with the reverse thereof facing the document scanning area without having to turn back the document while placed on the document loading tray. After the reverse side has been scanned, the document is returned with its sides inverted, after which the document is refed through the first and second transport paths, thereby allowing the remaining side, i.e. the top side, of the document to be scanned for exposure.
In the above-described construction in which a plurality of document sheets are sequentially fed to the scanning area, the timing to feed a succeeding document that follows the preceding document greatly affects the time that the whole copying operation takes. Therefore, there can be considered a construction in which the succeeding document is preliminarily fed to a standby position as close as possible to the preceding document while the preceding document is resting on the document scanning area and is being scanned by the optical scanning means, thereby attempting to shorten the time needed to transport a plurality of documents sequentially to the document scanning area. The construction in which the succeeding document is preliminarily fed to a standby position as described above is generally known as preliminary feeding.
An example of the preliminary feeding is disclosed in Japan Patent Publication No. 62-12533. According to the construction disclosed therein, when sequentially feeding a plurality of documents to the transparent plate which serves as the document scanning area, the preliminary feeding and inverting of a document is started after the preceding document has been transported to its rest position on the transparent plate. This means that the start of the preliminary feeding is late. Therefore, in the case of relatively small size documents, for example, the preliminary feeding of the succeeding document may not be properly completed during the scanning of the preceding document on the scanning area.
Furthermore, in the above preliminary feeding, the succeeding document is placed on standby just before reaching the transparent plate and is not allowed to enter the area of the transparent plate while the preceding document is resting on the transparent plate. Therefore, in the case of relatively small size documents, for example, the succeeding document cannot be transported to stand by at a position sufficiently close to the preceding document.
Thus, because of a delay in the start of the preliminary feeding and the insufficiency of the preliminary feeding, a considerable limit is encountered when attempting to reduce the time needed to sequentially transport a plurality of document sheets to the document scanning area.